This invention broadly concerns reinforced glass or glass-ceramic composites. It is specifically directed to a method of forming such composites by thermal pressing a glass-impregnated preform, for example, a stack of glass-impregnated plies, which may be prepared from sheets, films, mats, or the like.
Organic composites, that is, organic polymer matrices reinforced with fibers or whiskers, have been widely adopted because of their enhanced strength. More recently, attention has turned to composites with a glass or glass-ceramic matrix because of their capability for performance under more severe operating conditions than their organic counterparts. In particular, the inorganic matrix materials can withstand considerably higher temperatures. However, they have required development of quite different methods of composite formation.
Heretofore, glass and glass-ceramic composites have customarily been formed by a process known in the art as hot pressing. A body of material to be hot pressed is placed in a mold, heated to an elevated temperature to soften or melt the material, held for a predetermined time at temperature, and under pressure, and then cooled. Characteristically, the material is maintained under molding pressure at least throughout molding and cooling. This may take several hours, and necessarily ties up the pressing equipment for such extended period.
Technically, the hot pressing technique is quite satisfactory. It has been used for development studies and custom production. However, the tieup of equipment over an extended period of time is severely limiting as far as volume production is concerned.